The field of the invention generally relates to rotary drum vacuum washer filters for washing pulp and increasing the consistency (dewatering) of pulp in the pulp and paper industry, and for washing and dewatering suspensions of solids and liquids on other industries (such as but not limited to wastewater treatment, food processing, cement production and mining). In particular, the invention relates to a filtrate suction control valve for rotary drum vacuum washer filters.
Pulp is typically formed of wood chips or other cellulosic material. The pulp has been processed to separate the fibers in the cellulosic material. The pulp flows in a slurry. The rotary drum vacuum washer filter separates the pulp from the liquor in the slurry. The rotary drum vacuum washer filter is also referred to as a filter because it removes liquor and wash liquid from the pulp.
The removed liquor and wash liquid drain into a filtrate chamber at the end of the rotary drum and flow down a drop leg conduit. The downward flow of liquor and wash liquid create a suction that draws the liquor and wash liquid through the pulp mat and porous surface of the rotary drum.
The suction may be disrupted if excessive air or other gases are in the drop leg conduit. Air and gases fill the drainage channels of the rotary drum during a portion of the rotation of the drum. To prevent the air and gases in the drainage channels from entering the filtrate chamber and drop leg conduit, a valve is typically used to block the drainage channels while they are filled with air and gases. One type of conventional valve is mounted on a stem extending through a trunnion supporting an end of the rotary drum, as is shown in U.S. Pat. No. 7,981,248. Another type of valve is the conventional flat-face valve plate (no openings in the plate) that blocks the outlets to the drain channels during the portion of their rotation when the drain channels have large amounts of air or other gases.
To maintain high levels of suction in the rotary drum, air and gases should not flow into, or at least not become excessive in the filtrate chamber, elbow or drop leg conduit. A difficulty with the conventional flat-face valve plate is that air and other gases captured in the drain channels are released into the filtrate chamber as the drain channels pass the flat-face valve plate.